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Topic: Blocking The Viewfinder in a Long Exposure (Read 5306 times)

I was reading an article in a photo magazine and came across a tip I have seen before and wondered about its importance or usefulness. The recommendation was to close off the viewfinder when making a long exposure. As I considered that tip I remembered that Canon used to include a viewfinder cover which could be attached to the neck strap. In fact, I seem to recall that my F-1 had a switch which would close the viewfinder. But as I considered the necessity of using such an item I wondered if the mirror/body seal was so loose to allow light-leaks.

I rarely, if ever, take exposures of more than a second or two so I wondered if anyone who makes truly long exposures, say thirty seconds plus, has had an issue with light-leaks from the viewfinder?

I also seem to remember, back in the early days of light meters being part of the camera, that the measurement for light value was made in the pentaprism so the recommendation was to not allow any light to enter from the viewfinder side lest the exposure be skewed. Just some random thoughts on this early morning.

I make long exposures quite frequently (30s - 60s exposure time) and I never use the viewfinder cover. I can't see any negative impact on the final image.However if you have a bright light source behind you (eg. streetlamp) it could make a difference but if you can't read the top display of your camera without turning on the illumination it surely doesn't matter.

This image has an exposure time of 63s and I didn't use the viewfinder cover:

During the actual shoot, I often forget to cover the VF. I did not notice any significant change in the outcome of a shot with or without the cover on the VF. Maybe I was lucky to get away with it as I remember I never had any significant light source coming from behind the camera. Maybe I have not yet faced a scenario where you will need to cover the VF to get proper reading.

There's no need to cover the VF during an exposure (long or short) - the flipped-up mirror means no light from the VF reaches the sensor (assuming your camera isn't defective). But if you're not blocking the light with your eye at the VF during metering, light entering the VF can affect the metering, leading to an incorrectly exposed shot.

Current EOS bodies do come with that little rubber eyepiece cover that attaches to the strap, and you remove the eyecup to use it. The 1-series bodies have a built-in VF shutter (a little lever behind the eyecup) which is a handy feature. Before getting the 1D X, I'd usually just hang the lens cap from the eyecup instead of using the little rubber cover.

I was reading an article in a photo magazine and came across a tip I have seen before and wondered about its importance or usefulness. The recommendation was to close off the viewfinder when making a long exposure. As I considered that tip I remembered that Canon used to include a viewfinder cover which could be attached to the neck strap.

Canon includes viewfinder cover attached to the neck strap with the 5Dmk2 & mk3. I'd be surprised if xxD & xxxD models didn't have one as well.

But if you're not blocking the light with your eye at the VF during metering, light entering the VF can affect the metering, leading to an incorrectly exposed shot.

That's interesting (and makes sense) - do you know how often that happens and how severe the impact is? I sometimes "blind meter" tripod shows w/o my eye on the vf after already having mf'ed and when not wanting to engage live-view either to save battery or to avoid distraction by the lit screen. Maybe I should start putting my finger in front of the vf when metering?

But if you're not blocking the light with your eye at the VF during metering, light entering the VF can affect the metering, leading to an incorrectly exposed shot.

That's interesting (and makes sense) - do you know how often that happens and how severe the impact is? I sometimes "blind meter" tripod shows w/o my eye on the vf after already having mf'ed and when not wanting to engage live-view either to save battery or to avoid distraction by the lit screen. Maybe I should start putting my finger in front of the vf when metering?

It depends on how much light is shining on the back of the camera relative to the brightness of the scene. An effect of a stop or more is not uncommon.

Easy to demonstrate with an extreme situation - I just turned on my camera with the lens cap on, and closing the VF shutter dropped the metered exposure by 8.33 stops.

I rarely, if ever, take exposures of more than a second or two so I wondered if anyone who makes truly long exposures, say thirty seconds plus, has had an issue with light-leaks from the viewfinder?

I frequently shoot ultra long exposures (between 120s & 240s) at high noon with a 5D3+17-40mm f/4L+Hoya R72 filter combo and I do encounter light leaks whenever I forget to cover the viewfinder. To me, it boils down to the light intensity behind your camera.

I use gaffer tape to cover the eyepiece. The Canon rubber cover thingy gets popped out sometimes by the weight of my strap, and anyway I'm afraid I'll lose the eyecup. An eyepiece shutter would be great, tho; haven't had one of those since the T90.